Gfyuki

I'm trying to create a planet with a hot desert north and south pole but a cold equator. Is this possible? and if so how? And if it's heavily related to space how would night and day work on this place?

I don't want a high fantasy reason, the world having 2 suns, or a network of underground volcanoes that are only heating up the north and south but not the middle.

Starting with the Earth as a template:

• Move it closer to the sun


• Reduce axial tilt


• Add thick rings

Rings around a planet like Earth would last a few million years at best, but we've been around for less time than that.

The poles would be hot due to star proximity. The rings would reduce radiation on and close to the equator, making it cold.

Have an axis tilt [1] over 56° or under 124°

Between these points the poles and the equator switch climate. Technically speaking the poles simply have a higher thermal insulation average per year than the equator. This graphic shows the relationship between axial tilt (obliquity) and the yearly average temperature (insulation) for a given latitude.

I'm unsure where this graphic comes from. I encountered it via a Quora post and took a screenshot. I was unable to find said post again, so this is an uploaded version on the screenshot. Should anyone know the source, please link it in a comment.

Looking at the graphs having an axial tilt near the limits won't give you polar deserts (actually the poles would be tropical with a ring of deserts arround them, but some tweaking could reduce the rainforest to desert) and equatorial ice capes, but overally global moderate average temperatures. At 90° axial tilt the poles have the warmest average temperature and the equator the coldest.

Yet keep in mind that I'm talking about yearly averages. An object that is at absolute zero for half a year and at 273 C° for the other averages out to moderate 0 C°. At 90° this illustation isn't far from the fact. If one hemisphere on a 90° world experiences winter it also experiences night. Only night for 1/4 of the year. Vice versa for the other hemisphere and summer. Autum and spring will be moderate-ish.

The equator will be the coldest place on such a planet, but as the graph shows not nearly as cold as Earth's poles. I'm uncertain if permanent icecaps are possible and while they aren't out of the question a tundra belt seems more plausabile in most cases. The seasons in the region will be two "twilight" seasons in winter and summer and "rotation day" seasons in autumn and spring.

The poles will be deserts in the sense of desolate wastelands, swinging between the hottest and coldest points on the planet on a half-yearly basis. The intermediate seasons will be slightly more moderate, but the temperature difference will purge anything staying longer than these seasons.

How extreme the temperature differences will be depends on whether or not the circulation cells in the atmospere and the rotational forces creating them are stronger than the winds thermal pressures, which will try to redistribute warm air equally across the surface. This is what happens on tidally locked planets where similar temperature differences can be found according to the latest simulations. I wasn't able to find any material on this case so choose whatever fits you needs.

Conclusion

Changing axial tilt is by far the easiest way to achive your goal. My recommendation would be to place the planet near the outer edge if the habitable zone to make the equator as cold as possible, raising the plausibility of an ice shild surviving the intermediate seasons. The poles will still be deserts going from frying ot freezing, but that's a cool extra. Tilt wise I would stick close to 90°, keeping the equator as cold as possible and making the seasonal cycle simple. While nothing short of a climate simulation will give you the full picture, this video [2] might help.

For further reading I would recommend this paper [3] on versions of Earth with different axial tilt.

[1] https://en.m.wikipedia.org/wiki/Axial_tilt

[2] https://youtu.be/J4K3H9aNLpE

[3] https://www.youtube.com/redirect?event=video_description&html_redirect=1&redir_token=3JAkHxRedLFbHxzvUdN1gVlo-1p8MTU1NjYxOTY0MUAxNTU2NTMzMjQx&q=http%3A%2F%2Fgoo.gl%2FQGA6Ga&v=J4K3H9aNLpE (Pdf)

Physics is not your friend here, the equator gets more sunlight coming in at a more vertical angle and passing through less atmosphere. This means higher temperatures.

The one thing that does counteract that is altitude, so the solution to your problem is to have a very high plateau or mountain range that happens to run roughly around the equator of the planet. Just think of the Himalayas for example which are at the same latitude as Egypt and India and yet have permanent snow cover.

It would be an odd coincidence to have it run like that and continental drift over millions or billions of years would change things but for several million years you could have a mostly cold equator with maybe occasional warmer valleys where the altitude drops and obviously if you had any coasts or oceans they would be tropical.

If you don't insist that your polar desert be hot, look no further than Earth.

The South Polar Plateau in Antarctica is one of the most arid landmasses on Earth, with annual precipitation of about 7 cm of snow (convert that to liquid, and that's drier than the Atacama Desert in Chile and Peru). The northern ice cap is similarly arid, though it's harder to notice with the sea ice (formed by surface freezing of sea water, for the most part).

Move the Earth a couple million miles further from the sun, and the poles will get even drier (less water evaporating from the oceans).

While it is improbable that a planet like this would exist given that we have not yet observed one in our universe. Having the planet's axis of rotation be a line tangent to it's orbital path would move your equator to be a band that would run through where the poles are on Earth while the new poles would be on the right and left sides of the planet.